1. Field of the Invention
The present invention relates to a semiconductor device, and, more particularly, to a semiconductor device suitable to be fabricated by a processing method involving plasma.
2. Description of the Related Art
Conventionally, a protective diode is connected to a wiring layer which connects the input/output (I/O) pad to an integrated circuit (IC) portion as one means to protect a thin insulating film, such as the gate insulating film of a MOSFET which is one of the elements constituting an integrated circuit, against an excess voltage.
When a positive excess voltage is supplied to the I/O pad, for example, the protective diode breaks down to permit a current to flow to a low-potential power supply V.sub.SS, thus absorbing the positive excess voltage. When a negative excess voltage is supplied to the I/O pad, the protective diode also breaks down to permit a current to flow to a high-potential power supply V.sub.DD, thus absorbing the negative excess voltage.
Such a protective diode works effectively with respect to the positive and negative excess voltages only when the power supply potentials are fixed to V.sub.DD and V.sub.SS. The protective diode does not perform the protecting function when only the substrate potential is fixed and the I/O pad or internal wiring layer are in a floating state as during the fabrication of the device. If charged particles contact the wiring layer in a floating state while processing a semiconductor device by a method using the charged particles such as a plasma method, charge-up occurs in the wiring layer, damaging a thin insulating film, such as the gate insulating film of a MOSFET that is a constituent of the IC. When the insulating film in the IC is damaged, an insulation defect like short-circuiting occurs, making the semiconductor device defective.
As described above, the I/O pad and the internal wiring layer are in a floating state during fabrication of the conventional semiconductor device (wafer processing), so that if charged particles hit against the conductive layer constituting the I/O pad and internal wiring layer, the conductive layer would be charged up. If charge-up occurs in the conductive layer, thin insulating films such as the gate insulating films of MOSFETs constituting an IC may break down.